Coat a pan with butter. Spread Nutella on one side of the sandwich. Lay the plain side of the bread on the pan. Place mini marshmallows on top of the slice in the pan while it cooks. Spread more Nutella on another piece of bread. Place on top of the slice in the pan. Butter the top, then flip the sandwich in the pan. Cook until the bread is toasted and the marshmallows have melted. Dip in jam or drizzle maple syrup over sandwich if desired. Enjoy!